1. Field of Invention
This invention relates to a method of measuring the magnetic fields of a recorded surface and more particularly to a method of measuring the magnetic fields of magnetically recorded information using a scanning tunneling microscope.
2. Description of Related Art
One of the most active areas in magnetic recording technology is the study of processes occurring at the microscopic level. In recent years, several techniques based on scanning tunneling microscopy have been developed to study magnetization patterns in recording media with sub-micron resolution. These include magnetic force microscopy (MFM), and tunneling stabilized (TS) or magnetic force scanning tunneling microscopy (MFSTM).
In "Tunneling-stabilized Magnetic Force Microscopy of Bit Tracks on a Hard Disk," a published article by P. Rice and J. Moreland in IEEE Trans. Magn., vol. Mag-27, 1991, pp. 3452-3454 it was shown that magnetic data on a hard disk can be imaged with a tunneling microscope by using a flexible triangular probe cut from a thin film of magnetic material.
In U.S. Pat. No. 4,791,368, entitled "Automatic Magnetic Field Measuring Apparatus Using NMR Principles," a method of more accurately measuring magnetic fields is described which entails surrounding the item being measured with a coil, initially measuring the magnetic field, estimating the magnetic resonance frequency of the item being measured, applying a high-frequency voltage of the estimated magnetic resonance frequency, iteratively refining the estimate of the magnetic resonance frequency until the variation in coil inductance is a maximum, and finally, from the resulting magnetic resonance frequency, calculating the magnetic field of the item being measured.
In U.S. Pat. No. 4,710,715, entitled "Method Of Mapping Magnetic Field Strength And Tipping Pulse Accuracy Of An NMR Imager," a method of checking the homogeneity of a magnetic field by producing contour lines of equal field strength is disclosed that utilizes a different preparation phase for NMR imaging. The new preparation phase consists of tipping the spins of the volume elements with a 90 degree wait 90 degree RF pulse sequence.
In U.S. Pat. No. 4,625,166, entitled "Method For Measuring Magnetic Potentials Using Hall Probes," a method of measuring the hysteresis curve of a magnetic material is disclosed. The steps of the method include subjecting the material to a magnetic field, summing the voltages from a plurality of Hall probes that are spaced in an arc, obtaining the magnetic flux density in the material, and deriving a hysteresis curve of the material from the magnetic flux density and the magnetic field intensity.
In U.S. Pat. No. 4,567,439, entitled "Apparatus For Measuring The Magnitude Of A Magnetic Field," a method of measuring the magnitude of a magnetic field is disclosed. The steps of the method include magnetizing the item, inducing an oscillating magnetic field, permitting free precession, inducing signals during free precession, and producing an output that is proportional to the frequency deviation of the induced signals.
In U.S. Pat. No. 4,232,265, entitled "Device For Measuring Intensity Of Magnetic Or Electromagnetic Fields Using Strain Gauges Mounted On Ferromagnetic Plates," a device is disclosed that measures magnetic fields by monitoring the electrical signal produced by strain gauges which are connected to overlapping ferromagnetic plates. The magnetic field to be measured causes the gap between the plates to change which in turn causes the electrical output signal from the strain gauges to change. The magnitude of the electrical signal indicates the magnitude of the magnetic field.